Nowadays a miniaturization and a higher recording density of the HDD (Hard Disk Drive) are proceeding rapidly, and an increase in recording density is expected much more in the future. An increase in recording density of HDD can be implemented by narrowing a width of the recording track to enhance a track density. However, when a track width is narrowed, a magnitude of recorded magnetization, i.e., amplitude of a recording signal, becomes small and thus an improvement in a reproducing sensitivity of the MR head (Magnetoresistive head) that reproduces a medium signal is required.
Recently the GMR head including a high-sensitivity spin valve film utilizing the GMR (Giant Magneto-Resistance effect) is employed. The spin valve film is a stacked film having such a sandwich structure that a non-magnetic spacer layer is put between two ferromagnetic layers, and a portion having a stacked film structure to produce a change in resistance is called a spin-dependent scattering unit. The magnetizing direction of one ferromagnetic layer (referred to as a “pin layer” or a “magnetization pinning layer” hereinafter) out of two ferromagnetic layers is fixed by the ferromagnetic layer, or the like. The magnetizing direction of the other ferromagnetic layer (referred to as a “free layer” or a “magnetization free layer” hereinafter) can be changed by the external magnetic field. In the spin valve film, a large magneto-resistance effect can be obtained by changing a relative angle of the magnetizing direction between two ferromagnetic layers.
As the magnetoresistive element using the spin valve film, there are the CIP (Current In Plane)-GMR element, the CPP (Current Perpendicular to Plane)-GMR element, and the TMR (Tunneling Magneto-Resistance) element. In the CIP-GMR element, a sense current is fed in parallel with a surface of the spin valve film. In the CPP-GMR element and the TMR element, a sense current is fed in the almost perpendicular direction to the surface of the spin valve film.
In the type that a current is fed perpendicularly to the film surface, a metal layer is used as the spacer layer in the normal CPP-GMR element, and an insulating layer is used as the spacer layer in the TMR element.
In the future, when a miniaturization of the magnetoresistive element is advanced with the increase in density of the magnetic head or the MRAM device, a higher MR ratio is required of the magnetoresistive element.
In order to improve the magneto-resistance effect, it is important to increase a spin-dependent scattering factor of the magnetization pinning layer and the magnetization free layer.